<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

</body>
<script>
    function currying(callback) {
        return function () {
            var _args = [...arguments];
            function func() {
                _args.push(...arguments)
                return func;
            }
            func.toString = func.valueOf = function () {
                console.log("toString", callback.apply(this, _args));
                return callback.apply(this, _args)
            }
            return func;
        }
    }

    function add() {
        return [].reduce.call(arguments, function (a, b) {
            return a + b;
        })
    }

    var sum = currying(add);
    var res = sum(1)(2)(3)(4);
    console.log("res", res);
    console.log(res*1);
    console.log(+res);
    console.log(String(res));
    console.log(res == 10);


</script>

</html>